Production of a purified alumina-silica product and substantially pure aluminum trichloride from bauxites and clays

ABSTRACT

At least a single stage chlorination system for the production of a substantially iron-free alumina-silica product from Bauxites, Bauxitic Clays and Clays wherein at least one chlorination agent is selected from the group consisting of Cl 2 , HCl and COCl 2  and at least one chlorination agent from the group consisting of AlCl 3  and SiCl 4 .

BACKGROUND OF THE INVENTION

This invention is a continuation-in-part of U.S. patent application Ser.No. 377,992 filed May 13, 1982.

The invention is primarily applicable to materials such as Bauxites andClays that have present as major impurities iron and titanium in variousmineral forms.

There has been a great deal of research and there is a vast quantity ofliterature in attempts to produce a relatively iron-free alumina,alumina-silica product and aluminum chloride from such raw materials asBauxites and Clays. None of the processes proposed have been shown to beeconomically successful.

This problem can best be described by the following references:Landsberg "Chlorination Kinetics of Aluminum Bearing Minerals:Metallurgical Transactions B, Volume 6B, June 1975; pps. 207-208."

"Whereas Foley and Tittle showed that iron could be removed frompre-reduced bauxite by chlorination to produce a refractory gradealumina, FIG. 2 indicates that a substantial loss of alumina accompaniesthe initial rapid iron chlorination under reducing conditions. Even ifthis loss could be tolerated the remaining iron is too high forproducing cell grade alumina or aluminum chloride."

U.S. Pat. No. 3,842,163, A. S. RUSSELL ET AL, entitled "Production ofAluminum Chloride" and assignors to Aluminum Company of America, state,to quote lines 45 to 58:

"In general, the reduction of aluminum-containing materials withchlorine in the presence of reducing carbon in some form to producealuminum chloride is an old and generally well-known reaction and one ofthe suggested expedients referred to above utilized Bauxite as thealumina containing material. Bauxite however, normally contains manyimpurities including iron oxide, silica, and titania. Since theseimpurities readily react with chlorine in the presence of carbon to formiron, silicon, and titanium chlorides, the usual gaseous aluminumchloride reaction effluent therefrom must be subjected to cumbersome andexpensive after-purification measues if these chloride contaminants areto be separated to provide even a reasonably pure aluminum product."

The U.S. Department of the Interior, Information Circular 1412 by RobertL. de Beauchamp, sums up the problem of producing AlCl₃ from variousmaterials on page 6, the last paragraph reading as follows:

"The raw materials that may be used for the preparation of AlCl₃,include bauxite, clays, shale, anorthosite, coal ash, and many otheraluminum containing materials. Bauxite or clays are the most logicalchoices because of their higher Al₂ O₃ contents and the large reservesof these materials available. Iron is the impurity most deleterious tothe process since it uses up chlorine and is difficult to remove fromthe product."

Canadian Pat. No. 569,830 to Groth in 1939 described a method forchlorinating aluminiferous materials by treating dehydrated and crushedraw materials with aluminum chloride vapor at 600° C.-900° C., removinghot reaction gases containing iron chloride and titanium chloride,treating the residue with chlorine and a reducing agent, and processingthe recovered aluminum chloride vapor containing silicon chloride andcarbon monoxide at temperatures above 800° C. with alumina oraluminiferous materials free from iron and titanium. The gases recoveredfrom the chlorination process are oxidized to convert at least thechlorides or iron and titanium to their oxides prior to condensation.Therefore, because of the oxidation step, chlorides of the materials arenot recovered in reusable form. Further, the vapor mixture recoveredcannot be filuted with CO in order that the oxidation stage can becarried out.

Groth Column 1, lines 28 to 32 states:

"It is true that when processing between 900° C.-1150° C. titanium isremoved from the original material along with the iron in the form oftitanium tetrachloride, but only in small amounts unless a large excessof aluminum chloride is used."

Weston, U.S. Pat. No. 4,277,446, in the first chlorination stage,depends upon the use of excess aluminum chloride containing FeCl₃ thatis recovered from the circuit and returned to chlorinate the Fe₂ O₃. Toquote, Column 8, lines 30-34:

"(b) Excess AlCl₃ that is used is recovered at a low cost as an impureAlCl₃ containing FeCl₃ and returned to the Number One Chlorination Stagewithout any deleterious effects on chlorinating the contained iron andtitanium minerals."

Most surprisingly I have found that with the present invention theremoval of the Fe₂ O₃ from the raw material is far more effective thanfrom either the teachings of Groth or Weston and in effect, as shown inthe examples, has been reduced to a level which to the inventor'sknowledge, has never been achieved heretofore by differentialchlorination.

SUMMARY OF THE INVENTION

It is accordingly a primary object of the present invention to provide anovel and low cost process for the production of aluminum-siliconproducts substantially free of iron.

A further object of the present invention is to provide a novel and lowcost process for the production of a substantially pure aluminumtrichloride from Bauxites and Clays wherein the iron has previously beenremoved from the raw materials prior to mass chlorination with Cl₂ orCOCl₂ to produce aluminum trichloride.

In satisfaction of the foregoing objects and advantages there ispresented by this invention in its broadest concept a process for theproduction of a substantially iron free alumina-silica product, andsubstantially pure aluminum trichloride from various materialscontaining aluminum in the form of aluminum oxide minerals and complexaluminum minerals such as Kaolinite, that is Al₂ O₃. 2SiO₂.2H₂ O, theprocess comprising:

(a) Calcining the feed material prior to the first chlorination stage toremove free and chemically combined water, and where such minerals asKaolinite are present to break the chemical bond of Al₂ O₃, SiO₂, and H₂O, driving off the H₂ O as water vapor and forming amorphous Al₂ O₃ andamorphous SiO₂, which products respond differentially to chlorinationtreatment.

(b) Number One Chlorination Stage in which the agents are at least COand at least agent selected from the group consisting of Cl₂, COCl₂ andHCl and at least agent selected from the group consisting of SiCl₄ andAlCl₃.

Most surprisingly, I have found that by the use of minor or starvationquantities of these groups of agents in a first chlorination stage atleast 95% of the contained iron in the raw material can bedifferentially chlorinated. The temperature in this Number OneChlorination Stage is about 750° C. to about 1150° C.

The end solids product from this Number One Chlorination Stage will beAl₂ O₃ and SiO₂ substantially free of Fe₂ O₃ and highly desirous by therefractories industry.

(c) This end solids product may be further treated in a Number TwoChlorination Stage to produce a substantially iron free AlCl₃ by meanswell known to the Art using at least chlorination agents selected fromthe group consisting of Cl₂ and COCl₂, and reducing agents selected fromthe group consisting of C. and CO. The AlCl₃ is feed stock to the fusedsalt electrolytic cell for the production of aluminum metal.

If the contained iron in the feed material to the process is not removedprior to this Number Two Chlorination Stage normally a substantialportion of it will chlorinate under the Number Two Chlorination Stageconditions and finally report in the aluminum metal produced which isunacceptable in the production of a relatively pure aluminum metal. Allof the steps described beginning with the Calcination Stage may becarried out in fluo-solids reactors well known in the Art.

The following will define for clarity various terms used in describingthe invention:

Calcination--also known as dehydration--this terminology as used in thisapplication means the following:

(a) Removal of any free moisture as steam.

(b) Breaking down of the bond of water of crystallization in aluminumoxide minerals having the chemical analysis of Al₂ O₃ xH₂ O, wherein ahigh percentage of water of crystallization is driven off as steam.

(c) Breaking down of the chemical bond or bonds of complex aluminumminerals such as kaolinite, Al₂ O₃.2SiO₂.2H₂ O, wherein the H₂ O isdriven off as steam and the Al₂ O₃ and SiO₂ are converted into amorphousAl₂ O₃ and amorphous SiO₂ respectively. To accomplish satisfactorycalcination of Bauxites and Clays, a temperature range of 625° C. toabout 1100° C. may be used. It will be appreciated that theeffectiveness of the calcination step is a primary function oftemperature and time, the economic optimum being readily determined byanyone skilled in the Art.

This stage of the process uses conventional equipment well known in theArt, and consists of such equipment as horizontal rotary kilns, verticalshaft furnaces, and fluo-solids reactors with their auxiliary gasscrubbers and dust collection units.

Clays--generally refer to materials containing little or no Al₂ O₃.xH₂ Ominerals and the major aluminum mineral component is essentiallyKaolinite.

Iron and Titanium--the standard practice of the aluminum industry is toreport Fe and Ti analyses as Fe₂ O₃ and TiO₂. The iron and titaniumminerals contained in the aluminum bearing materials vary considerablyand are but rarely only in the form of Fe₂ O₃ and TiO₂. For instance themajor iron mineral in Arkansas Bauxite is siderite, FeCO₃, and thecommonest occuring form of titanium is as ilmenite, FeOTiO₂. When Irefer to percentages of Fe₂ O₃ and TiO₂ herein, I mean the chemicalanalyses of Fe and Ti converted to Fe₂ O₃ and TiO₂ respectively.

Carbon--any form of carbon that can be used in specific stages of theprocess of the invention as a reducing agent for the contained metallicoxides in the raw material used in the process herein described, andthat will not introduce added impurities that may have a majordetrimental effect on the final desired product.

Examples of such carbon are charcoal, devolatilized coal coke, anddevolatilized petroleum coke. The type of coke used should be carefullyselected to avoid introducing comparatively large quantities ofimpurities that may have a major detrimental effect in the process toproduce pure aluminum trichloride.

Devolatilization--refers to solid fuels such as coal or petroleum cokewherein the specific material has been heated to a sufficiently hightemperature to drive off substantially all of the contained water aswater vapor and any free hydrogen contained in the raw material.

Neutral conditions--where there is just sufficient free oxygen to meetthe needs of the reaction.

Oxidizing conditions--where there is an excess of free oxygen to meetthe needs of the reaction and free oxygen present at the end of theparticular stage.

Reducing conditions--where there is an excess of free carbon, CO, H₂, orCH radical present to meet the needs of the reaction.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is now made to the drawings accompanying the application whereit will be seen that FIG. 1 shows a preferred flowsheet of the inventionfor the production of an alumina-silica product substantially free ofiron and the further treatment of this product to produce aluminumtrichloride substantially free of ferric chloride and as feed stock forthe production of substantially pure aluminum metal.

FIG. 2 shows a preferred flowsheet of the invention treating the gaseousproduct produced by Number Two Chlorination Stage by passing the gaseousproduct through a charcoal or devolatized coke bed to convert thecontained CO₂ to CO.

The gas stream containing the CO, and after removal of the aluminumchloride, (not shown) is preferably cycled to the numbers one and twochlorination stages.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a preferred flowsheet of the invention. The prepared feedmaterial shown at 11 may have been pretreated by magnetic cobbing toremove part of the Fe₂ O₃ and where present ilmenite and biotite mica.Where ultra fines are present the feed material may have been granulatedor pelletized by conventional means to prevent losses in the gas streamsduring calcination or chlorination particularly when using fluo-solidsreactors.

The feed material is fed to the Calcining Stage 12 to remove freemoisture and water of crystallization. The equipment is conventional(not shown) consisting of such units as horizontal kilns, shaftfurnaces, and fluo-solids reactors. In the calcination stage 12 and inthe at least two chlorination stages shown at 13 and 18 my preferredequipment (not shown) is fluo-solids reactors. From the CalcinationStage the material is fed to the Number One Chlorination Stage shown at13. In this stage as much as 98% of the Fe₂ O₃ in the material isdifferentially chlorinated with but minor to negligible amounts of thecontained Al₂ O₃. The solids product from the Number One ChlorinationStage is fed to the Number Two Chlorination Stage shown at 18 whereinthe solids product shown at 16, normally analyzes less than 0.03% Fe₂O₃, which is an unheard of purity for use in the refractory industrywhere the limiting Fe₂ O₃ specification is of utmost importance.

Where it is desirous to produce an aluminum chloride productsubstantially free of iron the solids product 14 is fed to the NumberTwo Chlorination Stage shown at 18. This stage involves masschlorination of the contained alumina normally using largeconcentrations of Cl₂ either as Cl₂ or COCl₂ and in the presence ofreducing agents preferrably selected from the group consisting of C. andCO.

The solids product shown at 19 consists of amorphous silica and minoramounts of alumina and is either a waste product or maybe marketed as,primarily, filler.

The gaseous product shown at 20 will contain the desired aluminumchloride plus minor amounts of SiCl₄, TiCl₄, Cl₂, CO₂ and CO, and traceamounts of FeCl₃.

As the volatilization temperatures of the AlCl₃, SiCl₄ and TiCl₄ are183° C., 59° C. and 137° C. respectively there is no problem in theirseparation from each other and from the CO₂, CO and Cl₂.

The FeCl₃ has a vapor solubility in the AlCl₃ and thus it is of theutmost importance to reduce the Fe₂ O₃ in the feed material to theNumber Two Chlorination Stage to the lowest possible level which in theinvention has been demonstrated to be less than 0.02% or in excess of98% of the original Fe₂ O₃ contained in the feed material.

FIG. 2 shows a preferred flowsheet of the invention treating the gaseousproduct from Number Two Chlorination Stage. The gaseous product shown at21 is passed through one or more beds of charcoal or devolatilized cokeshown at 27 to convert CO₂ contained in the gas stream to CO. The gasstream discharging from the treatment stage is either treated bydifferential temperature condensation or fractional distillation or acombination of the two as shown at 29, and well known to the Art, toproduce as shown at 29 substantially pure AlCl₃ which is a saleableproduct in itself or may be fed to a fused salt electrolytic bath toproduce aluminum metal and the contained chlorine released and returnedto the Number Two Chlorination Stage. In addition the SiCl₄ may be soldas a commercial product with at least part cycled to the Numbers One orTwo or both Chlorination Stages. The TiCl₄ can be converted to eithertitania or titanium metal. The CO and Cl₂ remaining in the gas streamare preferably cycled to Numbers One and Two Chlorination Stages.

An alternate circuit shown at 22 to 26 separates the AlCl₃, SiCl₄ andTiCl₄ from the CO₂, CO, and Cl₂ prior to conversion of the CO₂ to CO. Ina preferred embodiment (not shown) the SiCl₄ is retained in the gasstream with the CO and Cl₂ thus supplying the requisite SiCl₄ to theNumber One Chlorination Stage.

EXAMPLES OF THE INVENTION

The following examples of the invention were carried out on a bulksample of Kaolinitic Clay from a deposit located in the south easternUnited States of America.

The sample as received was magnetically cobbed in a Colburne laboratoryhigh intensity magnetic laboratory unit, dried to approximately 5% freemoisture, crushed, put through a rolls and screened at 8 to 18 mesh and65 or 100 mesh to produce a product that was essentially minus 8 plus100 U.S. Standard. This product was calcined at 700° C. to 750° C., andafter calcination was the feed material to the following examples exceptwhere otherwise noted.

The chemical analysis of the calcined product was as follows:

    ______________________________________                                        Al.sub.2 O.sub.3                                                                        SiO.sub.2                                                                            Fe.sub.2 O.sub.3                                                                           TiO.sub.2                                                                          L.O.I.                                     ______________________________________                                        44.0      51.5   1.27         2.77 0.3                                        ______________________________________                                    

All of the examples were carried out in a 21/2 inch fluo-solids reactorusing batch charges of 250 grams.

The total gas volume used in all tests was kept reasonably constant at5.0 liters per minute calculated at 21.1° C., and adjusted to the 5.0liters with CO.

EXAMPLE 1

The following were conditions of this example:

Temperature in Number One Chlorination Stage, 913° C.

Agents used:

1.5 gms/min. HCl and

1.0 gms/min. SiCl₄ and make-up of gas stream to approximately 5.0liters/min. with CO.

Treatment time: 25 mins.

At the end of the 25 minute treatment of the solids feed the residualsolids product analyzed 0.016% Fe₂ O₃. This analysis shows that 98.7% ofthe Fe₂ O₃ in the feed material was chlorinated to produce asubstantially iron free alumina silica product.

This was an amazing result from the use of starvation quantities of HCland SiCl₄ and the short duration of the differential chlorinationtreatment. The alumina-silica product is outstanding in the low ironcontent for refractories and alternately in the production of aluminumchloride using the previously described number two mass chlorinationstage would produce a substantially iron-free aluminum chloride productsuitable for the production of aluminum metal.

EXAMPLE 2

The following were conditions of this example:

Temperature in Number One Chlorination Stage, 925° C.

Agents used: 0.6 gms/min. HCl, 0.2 gms/min. Cl₂, 0.8 gms/min. SiCl₄ andmake-up of gas stream to approximately 5.0 liters/min. with CO.

Treatment time: 30 mins.

At the end of the 30 minute treatment of the solids feed the residualsolids product analyzed 0.029% Fe₂ O₃.

This analysis shows that 97.7% of the Fe₂ O₃ in the feed material waschlorinated to produce a substantially iron-free alumina-silica product.

EXAMPLE 3

The following were conditions of this example:

Temperature in Number One Chlorination Stage, 925° C.

Agents used: 0.8 gms/min. HCl, 1.0 gms/min. SiCl₄, 6.0 gms/min. AlCl₃and make-up of gas stream to approximately 5.0 liters/min. with CO.

Treatment time: 30 mins.

At the end of the 30 minutes treatment of the solids feed the residualsolids analyzed 0.027% Fe₂ O₃. This analysis shows that 97.9% of the Fe₂O₃ in the feed material was chlorinated to produce a substantiallyiron-free alumina-silica product.

The invention has been described herein with reference to certainpreferred embodiments. However, as obvious variations thereon willbecome apparent to those skilled in the Art, the invention is notconsidered limited thereto.

What I claim as my invention is:
 1. A process for the production of asubstantially iron free alumina-silica product from the group of rawmaterials consisting of kaolinitic clays and bauxites wherein saidkaolinitic clays contain at least kaolinite with the chemical analysisof Al₂ O₃.2SiO₂.2H₂ O and said bauxites contain at least one of theminerals with the chemical analysis of Al₂ O₃.xH₂ O and at least onesilica mineral from the group consisting of Al₂ O₃.2SiO₂.2H₂ O and SiO₂and said group of raw materials contain at least iron as iron mineral,the said process comprising:(a) subjecting the said prepared materialsto a calcining stage wherein the said materials are heated to within thetemperature range of 625° C. to about 1150° C. to remove free moistureand water of crystallization combined in said minerals contained in thesaid materials and to convert said aluminous and siliceous minerals toalumina and silica thus producing a solids alumina-silica ironcontaining calcined solids product; and (b) subsequently subjecting thesaid calcined solids product to at least one chlorination stage whereinthe said chlorination stage is carried out in the presence of starvationamounts of at least one chlorination agent selected from the groupconsisting of Cl₂, HCl and COCl₂ and at least one clorination agentselected from the group consisting of AlCl₃ and SiCl₄ and in thepresence of at least CO and in the temperature range of about 850° C. to1150° C. to produce a chlorinated alumina-silica product substantiallyfree of said iron.
 2. A process for the production of a substantiallyiron free aluminum chloride product from aluminous and siliceousminerals containing prepared materials, said materials consisting ofiron minerals containing Bauxites and Kaolinitic Clays comprising:(a)Subjecting the said prepared materials to a calcining stage wherein thesaid materials are heated to within the temperature range of 625° C. toabout 1150° C. to remove free moisture and water of crystallizationcombined in said minerals contained in the said materials and to convertsaid aluminous and siliceous minerals to alumina and silica thusproducing a solids alumina-silica iron containing calcined solidsproduct; (b) Subsequently subjecting the said calcined solids product toat least one chlorination stage wherein the said chlorination stage iscarried out in the presence of starvation amounts of at least onechlorination agent selected from the group consisting of Cl₂, HCl andCOCl₂ and at least one chlorination agent selected from the groupconsisting of AlCl₃ and SiCl₄ and in the presence of at least CO and inthe temperature range of about 850° C. to 1150° C. to produce achlorinated alumina silica product substantially free of said iron; and(c) Subsequently subjecting the said substantially iron freealumina-silica product to a further chlorination stage wherein the saidchlorination agent is selected from the group consisting of Cl₂ andCOCl₂ and in the presence of reducing agent selected from the groupconsisting of C. and CO. and in the temperature range of about 750° C.to 1150° C. to chlorinate the said alumina to subsequently produce analuminum chloride product substantially free of said iron.
 3. Theprocess of claims 1 or 2 wherein the said chlorination agent selectedfrom the group consisting of Cl₂, HCl, and COCl₂ is Cl₂ and HCl.
 4. Theprocess of claims 1 or 2 wherein the said chlorination agent selectedfrom the group consisting of Cl₂, HCl, and COCl₂ is COCl₂ and HCl. 5.The process of claims 1 or 2 wherein the said chlorination agentselected from the group consisting of Cl₂, HCl, and COCl₂ is HCl.
 6. Theprocess of claims 1 or 2 wherein the said chlorination agent selectedfrom the group consisting of Cl₂, HCl, and COCl₂ is Cl₂.
 7. The processof claims 1 or 2 wherein the said chlorination agent selected from thegroup consisting of Cl₂, HCl, and COCl₂ is COCl₂.
 8. The process ofclaims 1 or 2 wherein the said chlorination agent selected from thegroup consisting of AlCl₃ and SiCl₄ is AlCl₃.
 9. The process of claims 1or 2 wherein the said chlorination agent selected from the groupconsisting of AlCl₃ and SiCl₄ is SiCl₄.
 10. The process of claims 1 or 2wherein the said chlorination agent selected from the group consistingof AlCl₃ and SiCl₄ is AlCl₃ and SiCl₄.